Prior art servo-assemblies have included an axially-displacable servo-piston arranged in a cylindrical housing dividing the housing into two operating chambers or areas; an axial bore of the servo-piston includes an integral steering nut cooperating with a steering worm shaft or alternatively the servo-piston cooperates with a steering gear nut which is axially disposed and journaled in the servo-piston; the servo-piston includes a gear segment operatively connected to a toothed segment of a drive or power-output shaft; the gear segment being formed on a non-guided portion of the servo-piston and which has slight relative rotation in the housing in which is is supported; a steering shaft has a support portion sealingly surrounded by a cover which forms one side of an operational area of the assembly and the shaft extends axially from the cover; the cover includes an axially-projecting, cylindrical portion telescoping into the servo-piston or into a portion connected thereto; this cylindrical projection will support travel or movement of the servo-piston during its lift or work strokes.
Control cylinder assemblies of the general character described above, have incorporated a construction where the bore of the servo-piston is exposed at the cover, for example, and relatively large functional areas are provided during reciprocation of the servo-piston in opposed directions of movement. It is generally the case where a steering gear nut is incorporated in the servo-piston that a valving system is operated by a radially extending lever movable in response to servo-piston movement. If operating areas of different sizes are incorporated in the control assembly, i.e., 2:1 ratio, for example, then the interior of the servo-motor piston must be tightly sealed and be in communication with a pressureless area and this area is generally sealed by a lid sealing the opposed end of the bore of the servo-piston. The problem arising from such an arrangement is that there generally results an outward projecting extending at least one half the amount of lift or axial movement of the servo-piston. Depending upon the centered position of the servo-piston, there must also be present between the end of the steering worm shaft and the inner area of the lid a sufficient space or distance corresponding to one half the axial travel of the servo-piston. Furthermore, it is necessary to provide similar axial distances between the outer area of the lid and end wall of the housing.